Add automated upstream sync workflow

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QKxGW1raAWaqeU8WdHsMsp

.gitea/workflows/upstream-sync.yml

@@ -0,0 +1,46 @@
+name: upstream-sync
+
+on:
+  schedule:
+    - cron: "0 3 * * *"
+  workflow_dispatch:
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: quattro
+          fetch-depth: 0
+
+      - name: Fetch upstream and open sync PR
+        env:
+          TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          API: ${{ github.server_url }}/api/v1
+          REPO: ${{ github.repository }}
+        run: |
+          set -euo pipefail
+          git config user.name "omarchycn-sync"
+          git config user.email "sync@noreply.git.zacharyzhang.com"
+          git remote add upstream https://github.com/basecamp/omarchy.git
+          git fetch upstream quattro
+          UP=$(git rev-parse upstream/quattro)
+          echo "upstream quattro: $UP"
+          if git merge-base --is-ancestor "$UP" HEAD; then
+            echo "Already up to date with upstream"
+            exit 0
+          fi
+          BR="sync/upstream-${UP:0:8}"
+          if git ls-remote --exit-code --heads origin "$BR" > /dev/null; then
+            echo "Sync branch $BR already exists, PR pending review"
+            exit 0
+          fi
+          git checkout -b "$BR"
+          # Merge conflicts fail the job loudly; resolution is manual by design
+          git merge --no-edit "upstream/quattro"
+          git push origin "$BR"
+          curl -sS --fail-with-body -X POST \
+            -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
+            "$API/repos/$REPO/pulls" \
+            -d "{\"base\":\"quattro\",\"head\":\"$BR\",\"title\":\"Sync upstream omarchy ${UP:0:8}\",\"body\":\"Automated sync of basecamp/omarchy quattro @ $UP. Review changes, run ./test/all, then merge.\"}"